A four-line CCD (charge coupled device) sensor includes one monochrome CCD sensor and CCD sensors respectively for RGB. Each of the CCD sensors includes a photodiode array.
The number of photodiodes (photodiode elements) is the same among the four colors. This is equivalent to the fact that the resolution of the monochrome CCD sensor and the resolution of the color CCD sensors for the three colors are the same. The resolution indicates dpi (dot per inch).
An image reading apparatus according to a related art controls reading according to sample hold signals at the same timing among R, G, B, and K. The image reading apparatus is capable of controlling image data of R, G, B, and K using the same image enable signal.
If the image reading apparatus according to the related art includes a four-line CCD sensor of a hybrid type, in some cases, reading control for image data is complicated depending on line intervals of the four-line CCD sensor.
The CCD sensor of the hybrid type indicates a CCD sensor in which the resolution of a monochrome line and the resolution of color three lines are different. The line indicates a row of pixels for four colors.
For example, the four-line CCD sensor has line intervals: six lines between R pixels and G pixels, six lines between the G pixels and B pixels, and eight lines between the B pixels and K pixels. It is assumed that the four-line CCD sensor executes 50% reading.
The image reading apparatus according to the related art cannot read out a monochrome pixel on certain one line and color pixels on the line at the same timing. The image reading apparatus cannot execute inter-line correction in a state in which pixel data of four rows are aligned on the same line.
If the image reading apparatus performs reading at a reduction magnification with the four-line CCD sensor of the hybrid type, the image reading apparatus needs to generate a sample hold signal for R and B and a sample hold signal for G at different timings.
In shading correction performed by using the sample hold signals at the different timings, the image reading apparatus needs to perform control using an image enable signal for R and B and an image enable signal for G which is different from the image enable signal for R and B. The control is complicated.
In the image reading apparatus including the four-line CCD sensor of the hybrid type, it requires complicated control to read out pixel data of four lines at the same timing.